The present invention relates to a liquid crystal display device capable of reducing a consumption power.
As shown in FIG. 2, a liquid crystal display (LCD) controller 203 is connected with an LCD unit 205, an image data memory 202, a micro-processing unit (MPU) 201 and a synchronizing signal generator circuit 204. Under commands of MPU 201, image data stored in the image data memory 202 is input to the LCD controller 203 and is signal-converted, so that the converted image data is displayed on the LCD unit 205.
In a conventional LCD controller, when the same (frame) image data is displayed on the LCD unit for a long time, (1) the display is continued, or (2) after an input interruption from a keyboard a mouse or the like is monitored and a desired period of time elapses, driving of a liquid crystal is stopped after the displayed image data is restored in the memory, or a backlight unit is turned off.
In the same frame image display for a long time, a method other than an image data restorage to the memory and a turning off of a backlight unit does not provide power saving of an LCD unit. Therefore, a frame image storage method for providing power saving without using unnecessary memories is desired. Also, since a backlight unit is not always included in all LCD devices, a method for providing power saving in a case wherein the same frame image is displayed for a long time, other than turning off of the backlight unit, is desired.
The object of the present invention is to solve the above problem.
According to the present invention, a liquid crystal display device of FIG. 1 includes, a micro-processing unit (MPU) 101 for controlling a whole peripheral circuit, an image data memory 102 capable of storing two frame image data, an image data arranging circuit 103 for arranging two frame image data, an image data comparator circuit 104 capable of comparing two frame image data in bit units, a timer circuit 106, a liquid crystal display (LCD) unit 110, an LCD controller 107 for controlling the LCD unit 110, a synchronizing signal generator circuit 109 for generating synchronizing signals (vertical and horizontal synchronizing signals), and a synchronizing signal regulating circuit 108 for regulating vertical and horizontal synchronizing signals in accordance with an output signal from the circuit 104. An output signal from the circuit 108 is input to the LCD controller 107, to control synchronizing signals to the LCD unit 110.
In the above structure, a peripheral circuit in an LCD device represents a circuit having a function for driving a display portion constructing the LCD unit. The display portion in the LCD device has a structure which pixels constructed by a liquid crystal arranged between at least one pair of electrodes are arranged at a matrix form. As a structure of the display portion, there is two types. One is a simple matrix type, and the other is an active matrix type.
Basically, an LCD unit includes analog buffers for driving each liquid crystal pixel arranged at a matrix form, analog memories for storing images to be displayed, and shift registers for generating operation timings of a matrix circuit in an X and Y directions. Also, a peripheral circuit in the LCD device includes an LCD controller for supplying data and clocks for the shift registers of X and Y directions to the LCD unit, a synchronizing signal generating circuit for supplying horizontal and vertical synchronizing signals and timing signals to the LCD controller, and an image data memory for storing images to be displayed.
The above structure can be used in a simple matrix type or an active matrix type LCD device. A liquid crystal material to be used is not limited to a specific material.
A memory element capable of storing two frame image data has a function for storing two frame image data necessary to display two frames. As the memory element, a video random access memory (VRAM) is used. The VRAM is of a dynamic random access memory (DRAM) and has normal parallel input and output ports, and further serial input and output ports.
Two frame image data stored in the image data memory 102 are compared with each other in bit units by the image data comparator circuit 104, and then the circuit 104 outputs an output signal representing a comparison result. In accordance with the output signal, the synchronizing signal regulator circuit 108 regulates horizontal and vertical synchronizing signals and supplies the regulated horizontal and vertical synchronizing signals to the LCD controller 107.
In a case wherein the same frame is displayed for a long time, if the number of scannings on a display portion (screen) of the LCD device is decreased, a consumption power can be reduced.
A time to decrease the number of scannings is set by the timer circuit 106, time interval that characteristics of a liquid crystal does not deteriorate without applying an alternating voltage to a liquid crystal in an LCD device, a refreshing time of a memory for storing image data in a peripheral circuit of the LCD device, or a refreshing time of an analog memory included in the LCD unit can be selected and set.